Multiple system atrophy (MSA) is a progressive, degenerative neurological disorder characterized by parkinsonism, ataxia & dysautonomia. The cardinal pathological feature of MSA is the presence of glial cytoplasmic inclusions composed of alpha-synuclein (SYN) in oligodendrocytes. Recent studies suggest that abnormal SYN accumulation in neurons & glia leads to cellular dysfunction & neurodegeneration. During the previous funding period we developed in vitro & in vivo models of MSA showing that mitochondrial damage & hyperphosphorylated SYN aggregate generation may contribute to the pathogensis of MSA. However, mechanisms by which these pathways promote oligodendrogial dysfunction & neurodegeneration are unclear. In this renewal we will investigate the role of mitochondrial dysfunction in SYN phosphorylation & toxicity. Our central hypothesis is that oxidative stress due to mitochondrial dysfuntion may promote G-protein coupled receptor kinase (GRK) activation & toxic SYN phosphorylation. The main objective is to investigate neurodegeneration in MSA-like SYN transgenic (tg) models to determine if reducing SYN accumulation represents a therapeutic strategy for MSA. Aim 1. In order to determine the role of hyperphosphorylated SYN accumulation in oligodendrocj^es in the mechanisms of neurotoxicity, we will analyze SYN accumulation & neurodegeneration in myelin basic protein (MBP)-SYN tg mice expressing wild-type (wt) human SYN or a nonphosphorylatable SYN mutant (S129A). MBP-SYNwt tg mice will be crossed with GRK2- or GRKS-deficient mice & MBP-SYNwt tg mice & MBP-SYN(S129A) tg mice will receive intra-cerebral infections with lentivirus expressing GRK2 or GRK5 under a oligodendroglial specific promoter (MBP). Aim 2. In order to determine the role of mitochondrial dysfunction & oxidative stress on GRK activation & SYN phosphorylation, MBP-SYN (wt and S129A) mice & oligodendroglial cells will be challenged with 3- nitropropionic acid. Aim 3. In order to determine if neuronal impairments in MSA models can be ameliorated by reducing SYN aggregation or inhibiting GRKs, MBP-SYN wt tg mice will be treated with rifampicin or GRK blockers. Behavioral performance, neurodegeneration, SYN oligomerization & phosphorylation & GRK activity will be assessed